Indirect fluorescence-based in situ geometry measurement for laser chemical machining

Optical geometry measurements of submerged workpiece surfaces in the chaotic fluid environment of laser chemical machining (LCM) are challenging, because the produced cavities feature high aspect ratios and surface gradients. To avoid reflection-based artefacts at high gradients, molecules are added to the acid, whose fluorescence is detected with a confocal setup. The model-based signal processing enables the indirect measurement of the micro-geometry even in acid layers with mm to cm thickness and is capable to cope with process-inherent bubbles. As a result, the geometry measurement is shown to be applicable for the LCM process at surface gradients up to 84°.